Today is your lucky day. It's your day for a perfect moment.
He sit down, puts his hand on the back of the bench, then rubs his eye.
*SNAP!* You're in.
Instantly you think small thoughts and are absorbed by the mucous membrane tissue of the eye and soon you find yourself in the nearest open section of tissue getting set to infect it thoroughly and as you begin your devious work--a threat looms.
You have been seen by a macrophage, the Sentinel of the human body tissues. When macrophages don't live in tissues they're called "phagocytes." Your eyes glint in anger as you let out a roar of dismay, infuriated that your plans have been thwarted. Then without warning, the small figure of an antibody attaches itself to you and sounds the alarm.
The immune system of the human host you're invading is immediately activated. All is lost.
In just a matter of moments phagocytes (or macrophages) descend on you and begin their process to entirely eliminate you. The first phagocyte to reach you wastes no time: he attaches you to himself and immediately ingests you into a bubble-like organelle (tiny organism) called a phagosome.
Once you've been entirely soaked up by him, a lysosome joins him and says "here, you need this" then in a move that makes short work of you, shoots you full of enzymes. You are helpless as you are digested by a team of organisms that just joined together to become a phagolysosome in order to destroy you. That lysosome, where did he come from? The endoplasmic reticulum (a part of a cell) created him just for that purpose. To join alongside the phagocyte and help him destroy you, the evil foreign invasion forces of disease that doesn't belong.
Within minutes you are not only destroyed, but you're also no more than an afterthought as your microbial remains are eliminated from the tissue Sentinel in a process called egestion.
Not stopping here, the phagocyte alerts the rest of the body by sending out a warning signal through antigenic determinants, a display that is shown on the phagocyte like a bright flag to alert the entire immune system as if to say "wake up! We're being invaded!"
The next morning the human body has changed from the day before--it feels like he has a cold, his throat is sore, and his right eye burns warmly. That burning sensation in his eye is called inflammation: it activates the immune system, sets the body in motion to repair itself in that area, and encourages any phagocytes in the area to come and destroy any microorganisms present.
Even before that human body goes to the doctor's to find out that he has "pink eye" or conjunctivitis, the body is hard at work destroying any of the bacteria that could left in the area and protecting the eye from any harm.
A macrophage destroying a bacteria.